Ink delivery system with gravity, valve and pump control of backpressure

ABSTRACT

An ink delivery system for supplying ink to an inkjet printhead at a predetermined backpressure. The ink delivery system includes: a pressure regulating valve connected to a printhead inlet port; an ink tank connected to a valve inlet of the pressure regulating valve; and a pump connected to a printhead outlet port. The backpressure of ink supplied to the printhead is controlled by: a height h 1  of ink in the ink tank relative to a valve orifice, a height h 2  of the valve orifice relative to the printhead, a position of a valve member relative to the orifice and a pump speed of the pump.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 63/174,988, entitled PRESSURE-REGULATING VALVEAND INK DELIVERY SYSTEM FOR INKJET PRINTHEAD, filed on Apr. 14, 2021,the disclosure of which is incorporated herein by reference in itsentirety for all purposes.

FIELD OF THE INVENTION

This invention relates to a pressure regulating valve for controllingpressure at an inkjet printhead. It has been developed primarily forsupplying ink to an inkjet printhead at a relatively constant pressure,as well as lowering the cost of ink delivery systems.

BACKGROUND OF THE INVENTION

Inkjet printers employing Memjet® technology are commercially availablefor a number of different printing formats, includingsmall-office-home-office (“SOHO”) printers, label printers andwideformat printers. Memjet® printers typically comprise one or morestationary inkjet printheads, which are user-replaceable. For example, aSOHO printer comprises a single user-replaceable multi-coloredprinthead, a high-speed inkjet press comprises a plurality ofuser-replaceable monochrome printheads aligned along a media feeddirection, and a wideformat printer comprises a plurality ofuser-replaceable printheads in a staggered overlapping arrangement so asto span across a wideformat pagewidth.

Supplying ink to multiple printheads can be problematic as the number ofprintheads increases. In order to maintain high print quality, eachprinthead should receive ink at about the same ink pressure from acommon ink reservoir.

U.S. Pat. No. 10,252,540, the contents of which are incorporate hereinby reference, describes an ink delivery system suitable for a digitalinkjet press having multiple printheads. This system uses gross pressurecontrol in a common ink delivery module and local fine pressure controlin each print module containing a respective printhead. Due to the highink flow requirements of multiple inkjet printheads as well as the needto control pressure in positive and negative pressure ink lines, twodiaphragm pumps are required for controlling ink pressure in the inkdelivery module. These diaphragm pumps are necessarily large, highquality pumps, which operate in combination with localelectronically-controlled pressure regulators in each print module.Accordingly, the ink delivery system is an expensive system due to thehigh cost of two diaphragm pumps as well the electronically-controlledpressure regulators in each print module.

For inkjet printing systems having a small number of print modules (e.g.one or two print modules), an expensive ink delivery module designed forlarger systems is undesirable and adds significantly to the overall costof the system. U.S. application Ser. No. 17/180,401 filed Feb. 19, 2021describes an ink delivery module suitable for inkjet printing systemshaving a small number of printheads. The ink delivery module uses alow-cost air pump cooperating with flow restrictors as a means forregulating pressures in an ink supply tank and an ink return tank, whichare connected to an ink supply line and an ink return line,respectively.

Passive pressure regulating valves have been proposed as a suitablemeans for controlling ink pressure in inkjet printing systems. Forexample, U.S. Pat. No. 7,712,880 (assigned to Memjet Technology Ltd)describes a pressure regulating valve having a diaphragm and a biasingmechanism, which cooperate to open and sealingly close a valve memberagainst a valve seat in response to ink pressure changes. U.S. Pat. No.7,862,138 (assigned to Hewlett-Packard Development Company, L.P.)describes a pressure regulating valve operating using a similarprinciple: a biased diaphragm is connected to a valve member via a levermechanism in order to sealingly close or open an orifice.

Pressure regulating valves have the advantages of low cost and localizedpressure control in proximity to the printhead. However, the valvesdescribed in the above-mentioned prior art suffer from the drawback ofhysteresis caused by sealingly closing and opening an orifice, as wellas fluctuating pressures. Furthermore, high flow rates cannot be readilyachieved via an opening and closing valve.

It would therefore be desirable to provide a low-cost means forregulating ink pressure, which at least ameliorates some of thedrawbacks of prior art pressure regulating systems described above.

SUMMARY OF THE INVENTION

In a first aspect, there is provided a pressure regulating valve for aninkjet printhead, said valve comprising:

an inlet port;

an outlet port;

a fluid flow path defined between the inlet port and the outlet port;

a first orifice positioned in the flow path, the first orifice having asealable first seat;

a movable first valve member configured for sealing engagement with thefirst seat;

a second orifice positioned in the flow path;

a movable second valve member configured for regulating a fluid flowrate through the second orifice;

a regulator chamber having the outlet port and comprising a diaphragmoperatively connected to the second valve member, such that movement ofthe diaphragm moves the second valve member relative to the secondorifice; and

a biasing mechanism for resiliently biasing the diaphragm away from thesecond orifice.

The pressure regulating valve according to the first aspect has theadvantage of controlling fluid flow to the printhead without requiring avalve member to function as a shut-off valve during idle periods of theprinthead. Advantageously, the shut-off function is handled by theactuated (e.g. solenoid actuated) first valve member, while thepressure-regulating function is handled by the diaphragm-controlledsecond valve member having no sealing or shut-off function.

Preferably, the second orifice is downstream of the first orifice.

Preferably, the first valve member comprises a compliant plug forsealing engagement with the first seat.

Preferably, the first valve member is operatively connected to anactuator, such as a solenoid, for opening and sealingly closing thefirst orifice. Typically, the first valve member is sealingly closedagainst the first orifice when the solenoid is powered down.

Preferably, the biasing mechanism comprises a spring operativelyconnected to the diaphragm, wherein the spring biases the second valvemember towards closure of the second orifice.

Preferably, in use, the diaphragm and the spring cooperate to passivelycontrol a flow rate through the second orifice. For example, contractionof the diaphragm towards the second orifice, caused by a reduction inpressure in the regulating chamber, tends to move the second valvemember towards opening of the second orifice. At the same time, thecontraction of the diaphragm is opposed by the bias of the spring,thereby providing passive regulation of the flow rate through the secondorifice via the balance of forces between the diaphragm and the spring.

Preferably, the second valve member and the second orifice have rigidengagement surfaces. The rigid engagement surfaces (e.g. metal, rigidplastics etc.) are typically non-sealing so as to avoid the surfacessticking and causing hysteresis in pressure management during use.

Preferably, movement of the diaphragm towards the second orificeprogressively opens the second orifice thereby to increase a flow ratetherethrough, and movement of the diaphragm away from the second orificeprogressively occludes the second orifice to decrease the flow ratetherethrough. Typically, the second orifice is not fully occluded (i.e.closed) during printing.

Preferably, a decrease in pressure in the regulator chamber moves thediaphragm towards the second orifice.

Preferably, an outer surface the second valve member is flared away fromthe diaphragm.

Preferably, the outer surface of the second valve member is non-linearlyflared.

Preferably, linear movement of the second valve member through thesecond orifice produces a linear change in an occluded area of thesecond orifice, such that the flow rate through the second orifice islinearly proportional to a distance moved by the second valve member.

In a related aspect, there is provided an inkjet printer comprising:

-   -   the pressure regulating valve as described above;    -   an ink tank connected to the inlet port; and    -   an inkjet printhead connected to the outlet port.

Preferably, the ink tank is positioned at a height above the pressureregulating valve for supplying ink at a positive pressure under gravityto the inlet port.

Preferably, the inkjet printhead pulls a negative ink pressure at theoutlet port during printing.

Preferably, a vacuum source connected to the inkjet printhead pulls anegative pressure at the outlet port during at least some non-printingperiods.

Preferably, in use, the pressure regulating valve maintains a negativeink pressure at the printhead within a predetermined pressure range.

Preferably, a level of ink in the ink tank is at a height h1 above theorifice; the orifice is positioned at a height h2 relative to theprinthead; and a backpressure of ink supplied to the printhead iscontrolled by: h1, h2, a position of the valve member relative to theorifice and a pump speed of a pump connected to a printhead outlet port.

In a second aspect, there is provided an ink delivery system forsupplying ink to an inkjet printhead at a predetermined backpressure,the ink delivery system comprising:

a pressure regulating valve having a valve outlet connected to aprinthead inlet port, the pressure regulating valve having apassively-controlled valve member for controlling a flow rate of inkthrough an orifice;

an ink tank connected to a valve inlet of the pressure regulating valve,the ink tank being positioned above the pressure regulating valve andthe printhead, the ink tank having an air vent open to atmosphere forsuppling ink to the pressure regulating valve under gravity; and

a pump connected to a printhead outlet port,

wherein:

a level of ink in the ink tank is at a height h₁ above the orifice;

the orifice is positioned at a height h₂ relative to the printhead; and

the backpressure of ink supplied to the printhead is controlled by: h₁,h₂, a position of the valve member relative to the orifice and a pumpspeed of the pump.

Preferably, the pump is connected to the ink tank via an ink returnline.

Preferably, the pressure regulating valve comprises:

-   -   a regulator chamber having a diaphragm operatively connected to        the valve member, such that movement of the diaphragm moves the        valve member relative to the orifice; and    -   a biasing mechanism for resiliently biasing the diaphragm away        from the orifice.

Preferably, the pressure regulating valve is as described above inconnection with the first aspect and preferred embodiments thereof.

Preferably, the height h₁ is controlled via one or more ink levelsensors cooperating with a refill pump receiving ink from a bulk inkreservoir.

Preferably, the pressure regulating valve is positioned above theprinthead. Alternatively, the pressure regulating valve is positionedbelow the printhead or at a same height as the printhead.

In a third aspect, there is provided a pressure regulating valve for aninkjet printhead, said valve comprising:

a valve inlet;

a valve outlet;

a fluid flow path defined between the valve inlet and the valve outlet;

an orifice positioned in the flow path;

a movable valve member configured for regulating a fluid flow ratethrough the orifice;

a regulator chamber having the valve outlet and comprising a diaphragmoperatively connected to the valve member, such that movement of thediaphragm moves the valve member relative to the orifice; and

a biasing mechanism for resiliently biasing the diaphragm away from theorifice, wherein an outer surface of the valve member is non-linearlyflared away from the diaphragm.

Preferably, linear movement of the valve member relative to the orificeproduces a linear change in an occluded area of the orifice, such thatthe flow rate through the orifice is linearly proportional to a distancemoved by the valve member.

Preferably, the biasing mechanism comprises a spring operativelyconnected to the diaphragm, wherein the spring biases the valve membertowards closure of the orifice.

Preferably, in use, the diaphragm and the spring cooperate to passivelycontrol a flow rate through the orifice.

Preferably, the valve member and the orifice have rigid engagementsurfaces.

Preferably, movement of the diaphragm towards the orifice progressivelyopens the orifice thereby to increase a flow rate therethrough, andmovement of the diaphragm away from the orifice progressively occludesthe orifice to decrease the flow rate therethrough.

Preferably, a decrease in pressure in the regulator chamber moves thediaphragm towards the orifice.

In a related aspect, there is provided an inkjet printing systemcomprising the pressure regulating valve, as described above inconnection with the first aspect.

As used herein, the term “ink” is taken to mean any printing fluid,which may be printed from an inkjet printhead. The ink may or may notcontain a colorant. Accordingly, the term “ink” may include conventionaldye-based or pigment-based inks, infrared inks, fixatives (e.g.pre-coats and finishers), 3D printing fluids (e.g. binder fluids),functional fluids (e.g. solar inks, sensing inks etc.) and the like.Where reference is made to fluids or printing fluids, this is notintended to limit the meaning of “ink” herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings, in which:

FIG. 1 shows an ink delivery system having a single printhead;

FIG. 2 shows an ink delivery system having two printheads;

FIG. 3 is a perspective of a pressure regulating valve;

FIG. 4 is a sectional perspective of the pressure regulating valve; and

FIG. 5 is a side view of a valve member for regulating flow rate throughan orifice.

DETAILED DESCRIPTION OF THE INVENTION Ink Delivery System

Referring to FIG. 1, there is shown schematically an ink delivery system1 for an inkjet printing system having a print module 2 comprising aninkjet printhead 4. The printhead 4 is typically a user-replaceablepagewide (or ‘linehead’) printhead of the type described in, forexample, US2011/0279566, U.S. Pat. No. 9,950,527 or 10,717,282, thecontents of which are incorporated herein by reference.

Ink is fed to the printhead 4 by means of an intermediary ink tank 6having a supply port 7 connected to a printhead inlet port 8 via an inksupply line 12. The intermediary ink tank 6 has a vent 14 open toatmosphere and feeds ink under gravity into the ink supply line 12. Theintermediary ink tank 6 may be configured for handling degassed ink, asdescribed in U.S. Pat. No. 10,639,903, the contents of which areincorporated herein by reference.

A return port 13 of the intermediary ink tank 6 is connected to aprinthead outlet port 16 via an ink return line 18. Hence, theintermediary ink tank 6, the ink supply line 12, the printhead 4 and theink return line 18 together form a closed fluidic loop. Typically, theink supply line 12 and the ink return line 18 are comprised of lengthsof flexible tubing.

The ink return line 18 has a circulation pump 20 (e.g. diaphragm pump)downstream of the printhead 4 for circulating ink around the closedfluidic loop.

The closed fluidic loop further comprises a degasser 22 in the inkreturn line 18 downstream of the pump 20 for degassing ink, a filter 23in the ink supply line 12 downstream of the intermediary ink tank 6 forfiltering ink supplied to the printhead 4, and a compliance 25 in theink return line between the printhead outlet 16 and the circulation pump20 for dampening ink pressure fluctuations. The filter 23 may be, forexample, of the type described in U.S. Pat. No. 10,369,802, the contentsof which are incorporated herein by reference. Alternatively, the filter23 may be integrated into the intermediary ink tank 6, as described inU.S. Provisional Application No. 62/990,911 filed Mar. 17, 2020, thecontents of which are incorporated herein by reference.

The ink delivery system 1 is designed to circulate ink around the closedfluidic loop, through the ink supply line 12 and the ink return line 18in a clockwise direction as shown in FIG. 1, during normal printing. Inthis way, ink can be continuously degassed and filtered to maintainoptimal print quality by minimizing air bubbles and particulatesentering the printhead 4.

Ink consumed by the printhead 4, either via normal printing ormaintenance operations, is replenished from a bulk ink reservoir 24,which feeds ink into the return line 18 via an ink refill line 26 havinga refill pump 28. Actuation of the refill pump 28 is controlled byfeedback from ‘high’ and ‘low’ ink level sensors 27A and 27B of theintermediary ink 6. When ink is sensed at predetermined ‘high’ level inthe intermediary ink tank 6, the refill pump 28 is deactuated; and whenink is sensed at a predetermined low′ level in the intermediary ink tank6, the refill pump is actuated so as to replenish ink in the closedfluidic loop from the bulk ink reservoir 24.

In order to deprime, isolate and/or replace the printhead 4, the printmodule 2 comprises an printhead shut-off valve 30 at an outlet side ofthe printhead 4 and an air intake line 32 controlled by an air shut-offvalve 34 at an inlet side. An upstream pressure regulating valve 50(described in detail hereinbelow), which additionally functions as anink shut-off valve is positioned in the ink supply line 12 between theintermediary ink tank 6 and the print module 2. Accordingly, when it isrequired to deprime the printhead 4 (for example, for printheadreplacement), the pressure regulating valve 50 is shut off while the airintake valve 34 is opened. Actuation of the circulation pump 20 pullsair through the printhead 4 thereby removing ink from internal inksupply channels. With ink removed from the printhead 4, the outletshut-off valve 30 is closed, thereby isolating the printhead andallowing it to be cleanly removed and replaced. Typically, the printhead4 is also isolated when the printing system is not in use by shuttingoff the pressure regulating valve 50 and the outlet shut-off valve 30.

For printhead priming operations, a vacuum capper (not shown) may beused in combination with the circulation pump 20 to draw ink through theink supply channels of the printhead and into nozzles, as described inU.S. application Ser. No. 17/174,090 filed Feb. 11, 2021, the contentsof which are incorporated herein by reference.

Pressure Regulation

As will be appreciated by those skilled in the art, it is important forthe printhead 4 to receive ink at a regulated, predeterminedbackpressure in order to operate optimally. With an ink pressure that istoo negative, ink pinned inside inkjet nozzles may be sucked back intothe printhead channels, thereby depriming the printhead; with an inkpressure that is too positive ink may flood from the inkjet nozzles ontothe nozzle plate of the printhead.

Gravity-fed ink delivery systems, such as those described in U.S. Pat.No. 10,639,903, have the advantage of passive control of backpressure.However, it is often inconvenient to position an intermediary ink tankbelow the printhead. In most inkjet printing systems, this space isoccupied by maintenance systems, media feed systems and the like.Furthermore, an intermediary ink tank feeding ink to multiple printheadscannot achieve accurate, localized pressure control for each printhead.

Active pressure control systems, such as those described in U.S. Pat.No. 10,252,540 have the advantage of accurate localized pressure controlwithout design constraints on the positioning of system components.However, such systems require expensive pumps and sensing circuitry thatmay not be economically feasible in smaller inkjet printing systems.

The ink delivery system 1 shown in FIG. 1 achieves localized passiveregulation of backpressure in the printhead 4, whilst employing anintermediary ink tank 6 positioned above the printhead. The backpressureexperienced at the printhead 4 is controlled by a combination of: aheight h₁ of the intermediary ink tank 6 relative to the pressureregulating valve 50, a passively controlled flow rate through an orificein the pressure regulating valve 50, a height h₂ of the pressureregulating valve relative to the printhead 4 and a pump speed of thedownstream pump 20. The pressure-regulating valve 50 is a criticalcomponent of this system having the dual functions of: passive pressureregulation via relative occlusion of an orifice; and an ink shut-offvalve for isolation of the printhead 4, deprime operations etc.

Furthermore, since the pressure-regulating valve 50 is designed as acompact, inexpensive component of the ink delivery system 1, then it maybe placed in close proximity to the printhead 4 and may, in someembodiments be incorporated into the print module 2, which is itself areplaceable module incorporating the replaceable printhead 4. Referringto FIG. 2, an ink delivery system incorporating two printheads 4connected in parallel has a respective pressure-regulating valve 50 foreach printhead, thereby providing local pressure control for eachprinthead from the common intermediary ink tank 6. In this way, if oneprinthead 4 has high ink demand relative to the other printhead, thenboth printheads can be maintained at a relatively equal ink pressure viaoperation of the respective pressure-regulating valves 50.

The pressure-regulating valve 50 will now be described in detail withreference to FIGS. 3 and 4. The pressure regulating valve 50 comprises avalve inlet 52, a valve outlet 54 and a fluid flow path definedtherebetween. A first orifice 56 is positioned in the flow pathdownstream of the valve inlet 52. The first orifice 56 has a first seat58, which is sealable by means of a movable first valve member 60 havinga compliant plug 62 configured for sealing engagement with the firstseat. As shown in FIG. 2, the first valve member 60 is shown in a shutposition whereby the compliant plug is sealed against the first seat 58.Movement of the first valve member 60 away from the first seat(downwards as shown in FIG. 2) unseats the valve member from the firstseat and opens the first orifice, allowing fluid to flow therethroughunder positive pressure from the valve inlet 52. Movement of the firstvalve member 60 between open and shut positions is controlled by anactuator in the form of solenoid 66. With the solenoid 66 actuated, thefirst valve member 60 moves away from the first seat 58 to open thefirst orifice 56; and the with the solenoid 66 deactuated, the firstvalve member 60 is sealed against the first seat 58 to close the firstorifice 56. The solenoid 66 is operated under the control of a separatecontroller (not shown) operatively connected to electrical terminals 68.Accordingly, the first orifice and first valve member, under the controlof the solenoid 66, function as a shut-off valve in the ink supply line12.

A second orifice 70 is positioned in the flow path downstream of thefirst orifice 56, the first and second orifices being connected via anintermediary flow channel 72. The second orifice 70 is defined in a baseof a regulator chamber 74, which forms an upper part of thepressure-regulating valve 50. The regulator chamber 74 comprises thevalve outlet 56 positioned in a sidewall thereof and a diaphragm 76positioned in a roof thereof. The diaphragm 76 is operatively connectedto a second valve member 78, which is slidably movable relative to thesecond orifice 70 so as to progressively occlude or progressively openthe second orifice. The second valve member 78 is biased away from thesecond orifice 70 by means of a spring 80 having one end connected tothe diaphragm 76 (and second valve member 78) and an opposite endconnected to a fixed support 82. In the embodiment shown in FIGS. 1 and2, the fixed support 82 is an external structure; however, it will beappreciated that the fixed support 82, having one end of the spring 80connected thereto, may be integrated into the roof of the regulatorchamber 74 with the spring extending through an internal roof cavity(not shown).

By virtue of the second valve member 78 being flared away from thediaphragm 76, movement of the second valve member towards the secondorifice 70 (i.e. downwards as shown in FIG. 4) results in progressiveopening of the second orifice, and movement of the second valve memberaway from the second orifice (i.e. upwards as shown in FIG. 4) resultsin progressively occlusion of the second orifice. As shown in FIG. 4,the second orifice 70 is shown in a closed position with the diaphragm76 unflexed. However, the second orifice 70 and second valve member 78have no function in shutting off the pressure-regulating valve 50 andfunction solely to regulate a flow rate of fluid through the secondorifice. Hence, the second valve member 78 and second orifice 70 haverigid engagement surfaces with no sealing function. Typically, thesecond valve member 78 and second orifice 70 are formed of metal and/orrigid plastics.

During printing, the first orifice 56 is open by means of actuation ofthe solenoid 66 and flow rate through the pressure-regulating valve 50is passively controlled by a position of the second valve member 78relative to the second orifice 70. With a high ink demand, the printhead4 pulls a relatively greater negative pressure at the valve outlet 54,thereby decreasing fluid pressure in the regulator chamber 74. Thisdecreased fluid pressure tends to flex the diaphragm 76 towards thesecond orifice 70 against the bias of the spring 80, thereby increasingthe flow rate of fluid through the second orifice. Conversely, when thefluid pressure in the regulator chamber 74 increases, the diaphragmflexes away from the second orifice 70, thereby decreasing the flow rateof fluid through the second orifice. Thus, the ink pressure experiencedat the printhead 4 is determined, at least in part, by the balance offorces between the flexing diaphragm 76 and the spring 80.

Advantageously, since the second valve member 78, which controls inkpressure at the printhead 4, has no shut-off function, problems ofhysteresis caused by an opening and closing valve, as well as problemsof valve-sticking are minimized.

In a preferred embodiment shown in FIG. 5, the outer surface of thesecond valve member 78 is non-linearly flared. For example, the secondvalve member 78 may be generally bell-shaped or trumpet-shaped, wherebya curved outer surface thereof determines an extent of occlusion of thesecond orifice 70. In this way, linear movement of the second valvemember 78 relative to the second orifice 70 produces a linear change ina non-occluded area of the second orifice. The non-occluded area of thesecond orifice 70 is proportional to the flow rate therethrough, suchthat the flow rate is linearly proportional to a distance moved by thesecond valve member 78 having, for example, a trumpet shape.

It will, of course, be appreciated that the present invention has beendescribed by way of example only and that modifications of detail may bemade within the scope of the invention, which is defined in theaccompanying claims.

1. An ink delivery system for supplying ink to an inkjet printhead at apredetermined backpressure, the ink delivery system comprising: apressure regulating valve having a valve outlet connected to a printheadinlet port, the pressure regulating valve having a passively-controlledvalve member for controlling a flow rate of ink through an orifice; anink tank connected to a valve inlet of the pressure regulating valve,the ink tank being positioned above the pressure regulating valve andthe printhead, the ink tank having an air vent open to atmosphere forsuppling ink to the pressure regulating valve under gravity; and a pumpconnected to a printhead outlet port, wherein: a level of ink in the inktank is at a height h₁ above the orifice; the orifice is positioned at aheight h₂ relative to the printhead; and the backpressure of inksupplied to the printhead is controlled by: h₁, h₂, a position of thevalve member relative to the orifice and a pump speed of the pump. 2.The ink delivery system of claim 1, wherein the pump is connected to theink tank via an ink return line.
 3. The ink delivery system of claim 1,wherein the pressure regulating valve comprises: a regulator chamberhaving a diaphragm operatively connected to the valve member, such thatmovement of the diaphragm moves the valve member relative to theorifice; and a biasing mechanism for resiliently biasing the diaphragmaway from the orifice.
 4. The ink delivery system of claim 1, whereinthe biasing mechanism comprises a spring operatively connected to thediaphragm, wherein the spring biases the valve member towards closure ofthe orifice.
 5. The ink delivery system of claim 4, wherein, in use, thediaphragm and the spring cooperate to passively control a flow ratethrough the orifice.
 6. The ink delivery system of claim 1, whereinmovement of the diaphragm towards the orifice progressively opens theorifice thereby to increase a flow rate therethrough, and movement ofthe diaphragm away from the orifice progressively occludes the orificeto decrease the flow rate therethrough.
 7. The ink delivery system ofclaim 6, wherein a decrease in pressure in the regulator chamber movesthe diaphragm towards the orifice.
 8. The ink delivery system of claim7, wherein an outer surface the valve member is flared away from thediaphragm.
 9. The ink delivery system of claim 7, wherein the outersurface of the valve member is non-linearly flared.
 10. The ink deliverysystem of claim 7, wherein linear movement of the valve member relativeto the orifice produces a linear change in an occluded area of theorifice, such that the flow rate through the orifice is linearlyproportional to a distance moved by the valve member.
 11. The inkdelivery system of claim 1, wherein the height h₁ is controlled via oneor more ink level sensors cooperating with a refill pump receiving inkfrom a bulk ink reservoir.
 12. The ink delivery system of claim 1,wherein the pressure regulating valve is positioned above or below theprinthead.
 13. The ink delivery system of claim 1 comprising a pluralityof printheads, each printhead and a corresponding plurality of pressureregulating valves, each printhead and respective pressure regulatingvalve being connected in parallel to a common ink tank.